1. Field of the Invention
The present invention relates to a zoom lens, or a zoom lens barrel, that can be used in digital cameras, and more specifically, to a zoom lens assembling mechanism which makes it easy for the zoom lens to be assembled and disassembled.
2. Description of the Related Art
A zoom lens, or a zoom lens barrel, having a movable barrel (e.g., a cam barrel) that is supported to be movable in the direction of the optical axis of the zoom lens while rotating about the optical axis relative to a stationary barrel of the zoom lens is known in the art. Such a zoom lens having a mechanism with which the movable barrel can be dismounted from the stationary barrel by rotating the movable barrel up to a position (disassembling position) toward the front of the operating range of the movable barrel, which includes the zooming range of the movable barrel, is also known in the art. The opposite ends of the zooming range of the movable barrel correspond to the wide-angle position and the telephoto position of the movable barrel, respectively. In a zoom lens having such a mechanism, the amount of overlap between the movable barrel and the stationary barrel in the optical axis direction (i.e., the length of supporting part of the stationary barrel for the movable barrel) becomes smaller as the movable barrel moves toward the front of the operating range thereof. Therefore, when the movable barrel is moved to the maximum extended position in the operating range thereof, the strength between the movable barrel and the stationary barrel for supporting the movable barrel by the stationary barrel is low, so that there is a possibility of the movable barrel being eccentric and/or tilting with respect to the optical axis, and/or deviating in the optical axis direction. For instance, in the case where the movable barrel and the stationary barrel are engaged with each other via male and female helicoids (helicoidal threads) respectively formed on the movable barrel and the stationary barrel, a sufficient amount of engagement between the male and female helicoids cannot be ensured when the movable barrel is moved to the maximum extended position in the operating range thereof, which reduces the strength between the movable barrel and the stationary barrel for supporting the movable barrel by the stationary barrel. If the movable barrel is eccentric and/or tilts with respect to the optical axis, and/or deviates in the optical axis direction, the lens group or groups which are supported inside the movable barrel cannot stay at their right positions, which deteriorates the optical performance of the zoom lens.
Upon assembly, every lens element of a digital camera must be optically centered, correctly spaced, and held firmly with a relatively high precision, e.g., tens times greater than that required in conventional cameras using light-sensitive film since object images are formed on the sensitive surface of a small CCD (CCD image sensor) which is much smaller than the picture plane of conventional cameras using light sensitive film. For instance, if the angle of view is constant, the focal length of a photographing lens becomes shorter as the size of the picture plane reduces, which in turn reduces the sizes of all the elements of the photographing lens such as lens elements, lens frames and other elements. Therefore, the influence that a tolerance (e.g., 10 xcexcm) has on a photographing lens system of a digital camera is much larger than the influence that the same tolerance would have on a photographing lens system of a conventional camera using light-sensitive film. Accordingly, manufacturing error which falls within tolerance of optical performance in the photographing optical system of a conventional camera using light-sensitive film can be outside the tolerance of optical performance in the photographing optical system of a digital camera.
To prevent such a deterioration of the optical performance from occurring, it is possible to increase the amount of overlap between the movable barrel and the stationary barrel in the optical axis direction (increasing the amount of engagement of male and female helicoids if the movable barrel and the stationary barrel are engaged with each other via male and female helicoids) when the movable barrel is in the maximum extended position in the operating range thereof to ensure a sufficient strength between the movable barrel and the stationary barrel for supporting the movable barrel by the stationary barrel. However, in this structure, the amount of rotational movement of the movable barrel from the frontmost position in the operating range to the disassembling position is great, which may impair the ease of assembly and disassembly of the zoom lens. In general, the movable barrel is coupled to a linear guide barrel to be rotatable about the optical axis relative to the linear guide barrel and to be movable in the optical axis direction together with the linear barrel, while the linear guide barrel is guided in the optical axis direction without rotating about the optical axis via linear guide grooves formed on the stationary barrel. Frictional resistance is generated between the linear guide barrel and the movable barrel when a driving force given to the movable barrel to rotate the same is converted into another driving force for moving the linear guide barrel linearly. Due to this fact, if the amount of rotational movement of the movable barrel from the frontmost position in the operating range to the disassembling position is great, the frictional resistance continues to be generated between the linear guide barrel and the movable barrel while the movable barrel is being moved all the way to the disassembling position when the movable barrel is dismounted from the stationary barrel. This reduces efficiency of assembly and disassembly of the zoom lens. Furthermore, if the amount of rotational movement of the movable barrel from the frontmost position in the operating range to the disassembling position is great, the movable barrel has to be rotated relative to the linear guide barrel to some degree in a range outside of the zooming range, which unnecessarily moves the lens group or groups supported within the linear guide barrel and the movable barrel. This is not preferable from the viewpoint of maintenance of the optical performance of the zoom lens and simplification of the lens group guiding structure of the zoom lens.
If the amount of overlap between the movable barrel and the stationary barrel in the optical axis direction is small, in some cases a light shield structure has to be provided between the movable barrel and the stationary barrel, since unwanted light can possibly enter into the zoom lens from a gap between the movable barrel and the stationary barrel. Moreover, in the case where linear guide slots for guiding the linear guide barrel in the optical axis direction without rotating the linear guide barrel about the optical axis are formed on the stationary barrel to extend along the length thereof, unwanted light can easily enter into the zoom lens from the linear guide slots.
The present invention has been devised in view of the above-described problems, wherein an object of the present invention is to provide a zoom lens assembling mechanism with which the optical performance of the zoom lens can be maintained, which prevents unwanted light from entering into the zoom lens from a gap between two barrels of the zoom lens, and which makes it easy for the zoom lens to be assembled and disassembled.
To achieve the object mentioned above, according to an aspect of the present invention, a zoom lens assembling mechanism is provided, including a stationary barrel having a female helicoid formed on an inner peripheral surface of the stationary barrel; a linear guide groove formed on the inner peripheral surface of the stationary barrel to cut across the female helicoid to extend parallel to an optical axis of the zoom lens; an inner inclined groove formed on the inner peripheral surface of the stationary barrel in front of the linear guide groove in an optical axis direction so that a major part of the inner inclined groove extends parallel to the threads of the female helicoid, so that one end of the inner inclined groove opens at a front end of the stationary barrel, and so that the other end of the inner inclined groove is connected with the linear guide groove; a movable barrel having a male helicoid formed on an outer peripheral surface of the movable barrel to mesh with the female helicoid, the movable barrel being moved forward and rearward in the optical axis direction while rotating about the optical axis in accordance with an engagement of the male helicoid with the female helicoid; a linear guide barrel guided to be movable together with the movable barrel in the optical axis direction and to be rotatable relative to the movable barrel about the optical axis; a linear guide projection formed on the linear guide barrel to be engaged in the linear guide groove, so that the linear guide projection can also be engaged in the inner inclined groove; and at least one lens group guided in the optical axis direction without rotating about the optical axis by the linear guide barrel to be moved in the optical axis direction in a predetermined moving manner in accordance with rotation of the movable barrel to change a focal length of the zoom lens. The linear guide barrel is guided in the optical axis direction with the linear guide projection being engaged in the linear guide groove when the movable barrel is positioned in an operating range, including a zooming range of the movable barrel, relative to the stationary barrel. The male helicoid and the female helicoid are engaged with each other by an amount of engagement in the optical axis direction which corresponds to a width in the optical axis direction of an area on the inner peripheral surface of the stationary barrel in which the inner inclined groove is formed when the movable barrel is positioned in a frontmost position thereof in the operating range. If the movable barrel is moved forward from the frontmost position relative to the stationary barrel in order to disassemble an assembly including the movable barrel and the linear guide barrel from the stationary barrel, the linear guide barrel moves forward in the optical axis direction, and at the same time, rotates together with the movable barrel about the optical axis while the linear guide projection slides along the inner inclined groove to thereby disassemble the assembly from the stationary barrel.
Preferably, the zoom lens further includes a rotational barrel positioned around the movable barrel, the rotational barrel being rotationally driven; a rotation transmission groove formed on the outer peripheral surface of the movable barrel to cut across the male helicoid to extend parallel to the optical axis; an outer inclined groove formed on the outer peripheral surface of the movable barrel behind the rotation transmission groove in the optical axis direction so that a major part of the outer inclined groove extends parallel to the threads of the male helicoid, so that one end of the outer inclined groove opens at a rear end of the movable barrel, and so that the other end of the outer inclined groove is connected with the rotation transmission groove; and an inward projection formed on the rotational barrel to be engaged in the rotation transmission groove, so that the inward projection can also be engaged in the outer inclined groove. Rotation of the rotational barrel is transmitted to the movable barrel with the inward projection being engaged in the rotation transmission groove when the movable barrel is positioned in the operating range relative to the stationary barrel. If the movable barrel is moved forward from the frontmost position relative to the stationary barrel in order to disassemble the assembly from the stationary barrel, the linear guide barrel moves forward in the optical axis direction, and at the same time, rotates together with the movable barrel about the optical axis while the inward projection slides along the outer inclined groove to thereby disassemble the assembly from the stationary barrel.
Preferably, the zoom lens assembling mechanism further includes a cam groove formed on an inner peripheral surface of the movable barrel so that a rear end of the cam groove opens at a rear end of the movable barrel; a linear guide slot formed on the linear guide barrel to extend parallel to the optical axis so that a rear end of the linear guide slot opens at a rear end of the linear guide barrel; a lens frame which holds the lens group; a cam follower formed on the lens frame to be engaged in the cam groove; and a linear guide projection formed on the lens frame to be engaged in the linear guide slot. The cam follower and the linear guide projection are respectively engaged in the cam groove and the linear guide slot, at rear ends thereof, when the assembly is moved forward from the stationary barrel to disassemble the assembly from the stationary barrel.
Preferably, the cam follower is formed on the linear guide projection.
In an embodiment, the zoom lens further includes a hood barrel positioned at the front of the zoom lens around the movable barrel, guided in the optical axis direction without rotating about the optical axis; an inward pin fixed to the hood barrel to project radially inwards; and a hood barrel guide groove formed on an outer peripheral surface of the movable barrel, the inward pin being engaged in the hood barrel guide groove so that the hood barrel moves in the optical axis direction via rotation of the movable barrel. The hood barrel guide groove includes an assembling section and an operating section connected to the assembling section so as to extend substantially along a circumferential direction of the movable barrel, wherein one end of the assembling section opens at the front end of the movable barrel. The operating section includes a zooming section in which rotation of the movable barrel causes the hood barrel to move forward and rearward in the optical axis direction. The rotation of the movable barrel causes the hood barrel to move forward and rearward in the optical axis direction to change a distance between a frontmost lens group of the lens group and the front end of the hood barrel in the optical axis direction in accordance with a variation of the focal length. The hood barrel can be disassembled from the front of the zoom lens by moving the inward pin forward to pull out the inward pin from the hood barrel guide groove when the inward pin is positioned in the one end of the assembling section. The assembly can be dismounted from the stationary barrel by being moved slightly forward from the frontmost position of the movable barrel relative to the stationary barrel when the movable barrel is positioned to have a predetermined rotational position relative to the stationary barrel so as to allow the hood barrel to be disassembled from the front of the zoom lens.
In an embodiment, the zoom lens further includes a barrier block fixed to the front end of the hood barrel and having at least one barrier blade for opening and closing a photographic aperture of the zoom lens.
In an embodiment, the linear guide groove, the inner inclined groove, and the linear guide projection respectively include a plurality of linear guide grooves, a plurality of inner inclined grooves, and a plurality of linear guide projections.
In an embodiment, the rotational transmission groove, the outer inclined groove, and the inward projection respectively include a plurality of rotational transmission grooves, a plurality of outer inclined grooves, and a plurality of inward projections.
The zoom lens can be incorporated in a digital camera.
According to another aspect of the present invention a zoom lens assembling mechanism is provided, including a stationary barrel; a movable barrel extending from the inside of the stationary barrel, and driven to move forward and rearward in an optical axis direction while rotating about the optical axis; a linear guide barrel guided to be movable together with the movable barrel in the optical axis direction and to be rotatable relative to the movable barrel about the optical axis; a linear guide mechanism, provided on the linear guide barrel and the stationary barrel, for guiding the linear guide barrel in the optical axis direction without rotating the linear guide barrel about the optical axis; and at least one lens group guided in the optical axis direction without rotating about the optical axis by the linear guide barrel to be moved in the optical axis direction in a predetermined moving manner in accordance with rotation of the movable barrel to change a focal length of the zoom lens. When the movable barrel is positioned in an operating range thereof including a zooming range of the movable barrel relative to the stationary barrel, the linear guide barrel is guided in the optical axis direction via the linear guide mechanism while the movable barrel moves together with the linear guide barrel in the optical axis direction while rotating about the optical axis relative to the linear guide barrel to move the at least one lens group in a predetermined moving manner. If the movable barrel is moved forward from a frontmost position of the operating range relative to the stationary barrel in order to disassemble an assembly including the movable barrel and the linear guide barrel from the stationary barrel, the linear guide barrel is no longer guided by the linear guide mechanism, and the linear guide barrel moves forward by a predetermined amount of movement in the optical axis direction while rotating together with the movable barrel about the optical axis to thereby disassemble the assembly from the stationary barrel.
Preferably, the zoom lens further includes a rotational barrel positioned around the movable barrel and driven to rotate; and a rotation transmission mechanism for transmitting rotation of the rotational barrel to the movable barrel. The rotation of the rotational barrel is transmitted to the movable barrel via the rotation transmission mechanism when the movable barrel is positioned in the operating range relative to the stationary barrel. If the movable barrel is moved forward from the frontmost position relative to the stationary barrel in order to disassemble the assembly from the stationary barrel, the rotation transmission mechanism is made inoperable between the rotational barrel and the movable barrel to thereby allow the assembly to be disassembled from the stationary barrel without rotating the rotational barrel about the optical axis.
Preferably, the stationary barrel includes a female helicoid formed on an inner peripheral surface of the stationary barrel. The movable barrel includes a male helicoid formed on an outer peripheral surface of the movable barrel to mesh with the female helicoid, the movable barrel being moved forward and rearward in the optical axis direction while rotating about the optical axis in accordance with an engagement of the male helicoid with the female helicoid.
Preferably, the zoom lens assembling mechanism further includes a cam groove formed on an inner peripheral surface of the movable barrel so that a rear end of the cam groove opens at a rear end of the movable barrel; a linear guide slot formed on the linear guide barrel to extend parallel to the optical axis so that a rear end of the linear guide slot opens at a rear end of the linear guide barrel; a lens frame which holds the lens group; a cam follower formed on the lens frame thereon to be engaged in the cam groove; and a linear guide projection formed on the lens frame to be engaged in the linear guide slot. The cam follower and the linear guide projection are respectively engaged in the cam groove and the linear guide slot, at rear ends, thereof when the assembly is moved forward from the stationary barrel to disassemble the assembly from the stationary barrel.
Preferably, the cam follower is formed on the linear guide projection.
In an embodiment, the zoom lens further includes a hood barrel positioned at the front of the zoom lens around the movable barrel, guided in the optical axis direction without rotating about the optical axis; an inward pin fixed to the hood barrel to project radially inwards; and a hood barrel guide groove formed on an outer peripheral surface of the movable barrel, the inward pin being engaged in the hood barrel guide groove so that the hood barrel moves in the optical axis direction via rotation of the movable barrel. The hood barrel guide groove includes an assembling section and an operating section connected to the assembling section so as to extend substantially along a circumferential direction of the movable barrel, wherein one end of the assembling section opens at the front end of the movable barrel. The operating section includes a zooming section in which rotation of the movable barrel causes the hood barrel to move forward and rearward in the optical axis direction. The rotation of the movable barrel causes the hood barrel to move forward and rearward in the optical axis direction to change a distance between a frontmost lens group of the lens groups and the front end of the hood barrel in the optical axis direction in accordance with a variation of the focal length. The hood barrel can be disassembled from the front of the zoom lens by moving the inward pin forward to pull out the inward pin from the hood barrel guide groove when the inward pin is positioned in the one end of the assembling section. The assembly can be dismounted from the stationary barrel by being moved slightly forward from the frontmost position of the movable barrel relative to the stationary barrel when the movable barrel is positioned to have a predetermined rotational position relative to the stationary barrel so as to allow the hood barrel to be disassembled from the front of the zoom lens.
In an embodiment, the zoom lens assembling mechanism further includes a barrier block fixed to the front end of the hood barrel and having at least one barrier blade for opening and closing a photographic aperture of the zoom lens.
In an embodiment, the linear guide mechanism includes a linear guide groove formed on an inner peripheral surface of the stationary barrel to extend parallel to an optical axis of the zoom lens; and a linear guide projection formed on the linear guide barrel to be engaged in the linear guide groove of the stationary barrel. The stationary barrel further includes an inner inclined groove formed on the inner peripheral surface thereof in front of the linear guide groove in an optical axis direction so that a major part of the inner inclined groove is inclined with respect to the linear guide groove, so that one end of the inner inclined groove opens at a front end of the stationary barrel, and so that the other end of the inner inclined groove is connected with the linear guide groove. When the movable barrel is positioned in the operating range thereof, the linear guide projection is engaged in the linear guide groove. In the case where the movable barrel is moved forward from the frontmost position of the operating range relative to the stationary barrel, the inner guide projection is inserted in the inner inclined groove, so that the linear guide barrel moves forward in the optical axis direction while rotating together with the movable barrel.
Preferably, the stationary barrel includes a female helicoid formed on the inner peripheral surface thereof, the threads of the female helicoid extending parallel to the inner inclined groove, wherein the movable barrel includes a male helicoid formed on an outer peripheral surface thereof to mesh with the female helicoid. The movable barrel is moved forward and rearward in the optical axis direction while rotating with respect to the stationary barrel, in accordance with an engagement of the male helicoid with the female helicoid.
The male helicoid and the female helicoid are engaged with each other when the linear guide projection is inserted in either the linear guide groove or the inner inclined groove.
The zoom lens can be incorporated in a digital camera.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-26705 (filed on Feb. 3, 2000) which is expressly incorporated herein by reference in its entirety.